Early experience plays an important role in shaping both how our brains represent the external world and how we interpret or perceive it. For example, while native English speakers readily categorize the syllables /ra/ and /la/, Japanese speakers with no exposure to English have difficulty distinguishing these two syllables. Whether or not listeners show such categorical perception can depend on the distribution of acoustical stimuli during development. Earlier studies have shown that when speech stimuli follow a bimodal distribution, categorical perception occurs;when speech stimuli follow a unimodal distribution, categorical perception does not occur. Proper early language exposure is critical to the development of language ability. Impoverished or improper language exposure can lead to language learning impairments. Understanding the relationship between developmental acoustic inputs, auditory cortex representations and perception is important in understanding language development and is the main goal of this proposal. We propose using the rat as a model system to study the role of stimulus statistics on cortical plasticity and perception. We are interested in how the statistics of acoustical stimuli can lead to changes in auditory cortex representations and how these changes could underlie categorical perception. In particular, this project will test the following hypotheses: 1) temporal repetition rates influence spectral plasticity in a single- tone environment, 2) statistical dependence in a two-tone environment determines how sounds are represented, and 3) categorical perception of sounds will occur only if their presentations is statistically independent. Rat pups will be reared in specific acoustic environments during development. To measure cortical representations, the primary auditory cortices of these animals will be mapped electrophysiologically. Sound discrimination and identification will be tested to assess categorical perception of tonal frequencies in these rats. Description of Relevance: Language skill is considered unique among humans, and our ability to communicate efficiently and effectively hinges on our language aptitude. Individuals who grow up with improper speech input can develop communication disorders. This research aims to understand the relationship between the acoustical environment, brain representation of sound, and perception.